(CNN)The National Transportation Safety Board says it is reviewing on-board video as well as data from the "black box" of the Amtrak Empire Builder train that derailed in rural Montana on Saturday, leaving three dead and at least seven hospitalized.
Eight cars from Amtrak's Empire Builder train 7/27 traveling from Chicago to Seattle/Portland jumped the tracks around 4 p.m. near Joplin, Amtrak said. Joplin is about 30 miles south of the Canadian border, with a population of about 150 people.
The train consisted of two locomotives and 10 cars and there were about 141 passengers and 16 crew members on board, the company said.
NTSB Vice Chair Bruce Landsberg says a team of 14 investigators and experts on the ground will review the train's front-facing video as well as video from the same vantage point on a freight train that passed through the area almost an hour and a half prior.
"We don't know that this point whether it was a track issue or an issue with the train, so all of these things are open," Landsberg said. "There's a lot of ground to cover and there is significant damage so our experts are going to be really looking at that."
Landsberg says train data shows it traveling between 75 and 78 miles per hour before it departed a right-curving section of track where the speed limit was 79 miles per hour.
Investigators will interview the train's crew as well as BNSF Railway track inspectors who conducted an inspection where the train left the tracks.
In a statement Sunday, Amtrak CEO Bill Flynn said the company was in mourning for those killed and injured.
"We have no words that can adequately express our sorrow for those who lost a loved one or who were hurt in this horrible event. They are in our thoughts and prayers," Flynn said.
He said Amtrak is "fully cooperating with the investigation" and working closely with the NTSB, Federal Railroad Administration, local law enforcement and response agencies.
"We share the sense of urgency to understand why the accident happened; however, until the investigation is complete, we will not comment further on the accident itself.
The NTSB will identify the cause or causes of this accident, and Amtrak commits to taking appropriate actions to prevent a similar accident in the future," the statement reads.
Passenger describes shock of derailment
Megan Vandervest, a passenger on a sleeper car on the train, had been taking a nap when the derailment jolted her awake.
"I would describe the experience as kind of extreme turbulence on an airplane but louder, and there was kind of a lot of smoke smell. The first thought I really had when I woke up was, 'Oh my God we're derailing,'" she told CNN.
"It was probably 10 or 15 seconds of rocking back and forth and tons of noise, and then we came to a stop. Really we didn't know what was going on for a couple minutes."
Vandervest said she was evacuated within 10 minutes of the incident and only then understood the extent of the damage.
"We kind of thought maybe the car behind us had slightly come off or something like that, but it ended up being much, much worse and a lot more jarring to see when we got off the train," she said. "The car behind ours was slightly off and then the one behind that was kind of in between two sets of railroad tracks, and the one behind that one had like completely tipped over and fallen over and that was kind of the most shocking part."
Seven people remain hospitalized
Injured passengers were taken by ambulance to nearby towns, with those in critical condition flown for treatment, said Amanda Frickel, the disaster and emergency services coordinator for Hill County.
Two patients remain hospitalized at Logan Health in Kalispell, according to hospital spokesperson Mellody Sharpton.
"Both patients are doing well enough to be discharged soon," Sharpton said.
Casey Husted, vice president of communications at Benefis Health System in Great Falls, told CNN that five patients remain at their hospital.
Husted told CNN that "they are in stable condition, although some require ICU level care."
Gov. Greg Gianforte offered "thoughts and prayers" to the individuals impacted by the "heartbreaking event."
"In the face of tragedy, Montanans did what they so best," Gianforte said at a news conference Sunday. He thanked the community at large for coming together, saying it was "an all of the Hi-Line effort."
The Empire Builder train travels between Chicago-St.Paul/Minneapolis and Spokane-Portland/Seattle, according to Amtrak's website, and offers passengers a chance to "experience the rugged splendor of the American West."
"Traveling between Chicago and the Pacific Northwest along major portions of the Lewis and Clark Trail, the mighty Empire Builder takes you on an exciting adventure through majestic wilderness, following in the footsteps of early pioneers," the website adds.
This article originally appeared on CNN